Neutral-to-ionic photoinduced phase transition of tetrathiafulvalene-p-chloranil by electronic and vibrational excitation: A real-time nuclear-electronic dynamics simulation study.

Tetrathiafulvalene-p-chloranil exhibits photoinduced phase transition (PIPT) between neutral (N) and ionic (I) phases, in which the constituent molecules are approximately charge-neutral and ionic, respectively. In addition to visible-light irradiation, which can induce both N → I and I → N PIPTs, infrared irradiation has been reported to induce the N → I PIPT. These results suggest that N → I and I → N PIPTs can be driven by electronic excitation, and the I → N PIPT can also be driven by vibrational excitation. However, the feasibility of the N → I PIPT using vibrational excitation remains an open question. In this study, we address this issue by simulating the PIPT processes using a nonadiabatic molecular dynamics approach combined with real-time electron dynamics at the level of a semiempirical quantum chemical model, density-functional tight binding. The results show the importance of vibronic interactions in the PIPT processes, thereby suggesting the possibility of N → I PIPT by vibrational excitations with infrared irradiation.